J. Chem. Eng. Data 1981, 26, 70-74
70
Table VI. Comparison of Distillation Data for Separation of Trioxane and Solventb
Moreover, benzene is more toxic than dichlorobenzene, and the allowable limits are 10 and 50 ppm, respectively ( 76). Hence, the expenses for safety precautions would be higher for benzene.
particulars dichlorobenzene benzene important solvent properties boiling point, " C 172- 179 80.1 specific gravity, d," 1.299 0.879 change in enthalpy (HT 5963 at 9960 114.5 at 80 H 2 9 8 ) kcal/kg-mol , toxicity (allowable limit), ppm wt % trioxane in distillate or bottom product min reflux ratio operating reflux ratio no. of theoretical stages condenser duty: kcal/h reboiler duty,' kcal/h
c (1)
0-,50
"C
75 99.9
10 99.9
0.5 1.0 11.8 2200 2500
1.0 1.5 24.9 4700 4900
P-3
Glossary
C P S W
(d
x,, xww
solute plait point solvent formaldehyde solution weight fraction of solvent in solvent layer weight fraction of formaldehyde solution in aqueous layer
LAerature Cited
'Calculated for processing extract, containing 10 kg/h trioxane. Trioxane bp 114.5 "C.
aldehyde and water contents being higher, the operating costs for purification of trioxane to bring it to the monomer grade would be more. Finally, trioxane has to be separated from the extracts by distillation. The data for the distillation from the extracts obtained at a solvent-to-feed ratio of 1.0 at 50 O C were calculated and are given in Table VI. The boiling points of benzene, odichlorobenzene, and trioxane are 80.1, 179, and 114.5 O C , respectively. Therefore, in the case of benzene extract, benzene would be the overhead product (at 80 'C) whereas, from the dichlorobenzene extract, trioxane would be distilled over at 114.5 OC. But in the former case the entire quantity of the benzene has to be separated by rectification. This would require a higher number of theoretical stages as well as operation at a higher reflux ratio. The consumption of energy will thus be higher. For the recovery of trioxane from dichlorobenzene extract, the requirements of theoretical stages, operating reflux, and heat load would be considerably lower.
(1) Sharan, K. M.; Sagu. M. L.; Swarup, Janardan Chem. Era 1976, 12, 283. (2) Charles, E. F. U.S. Patent 2304080; Chem. Abstr. 1949, 3 7 , 2748' (3) Joseph, F. W. U.S. Patent 2347447; Chem. Abstr. 1945, 3 9 , 91': (4) Natov, M.; Kabanvanov, V.; Godishink, M. M. Chem. Tech. Inst. 1961, 7 , 203. (5) Badlsche Aniline and Soda Fabrik A . G . (by Rolf Platz). Belgium Patent 620257; Chem. Abstr. 1963, 59, 7544A. (6) Adamek, M.; Dykyj, J.; a s k . S.; Gregor, F.; Kordk. J.; Patek, V. Czechosiovakie Patent 129711; Chem. Abstr. 1969, 71, 81440). (7) Dojcasky, J.; Neinrich, J.; Surovy. J. Chem. hum. 1969, 19, 413. (8) Yamase, Y.; Kutsuma, T. Japan Patent 7033184; Chem. Abstr. 1971, 74, 54361q. (9) DykyJi,J.; Kovac, A.; Ziak, J.; Ada&, M.; Gregor, F. Czechoslovakia Patent 138865; Ctwm. Abstr. 1971, 75, 36153q. (10) Sperber, H.; Fuchs, H.; Llbowitzky, H. German Patent 1688867; Chem. Abstr. 1972, 77, 114438~. (11) Sllvkin, L. G.; Orechkin, D. B.;Ovsyannikov, L. F. Khim. Prom. 1865, 41, 740. (12) Meissner, J. Bm. Chem. Eng. 1969, 14, 757. (13) Kuchhal, R. K.; Kumar, Basant; Mathur, H. S.; Gupta, P. L. Z . Anal. Chem. 1978, 294, 410. (14) Sherwood, T. K. "Absorptionand Extraction"; McGrawHill: New York, 1937; p 242. (15) Othmer, D. F.; Tobias, P. S. Ind. Eng. Chem. 1942, 34, 693. (16) "Occupational Exposure Umns for Airborne Toxic Substances"; Occupational Safety and Health Series no. 37, International Labour Office, Geneva, Switzerland, 1977. Received for review October 30, 1979. Accepted July 30, 1980.
Heat Capacity and Enthalpy of Phosphoric Acid Basil B. Luff Division of Chemical Development, National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, Alabama 35660
Measurements of the heat capacity of phosphoric acid were made over the ranges of concentratlon of 61.8-83.0% and temperature of 25-367 OC. A possible transition was found at -77 'C. Values for enthalpy were derlved. Previous studies ( 7) of the enthalpies of phosphoric acids and the derived heat capacities were made by using a high-temperature drop calorimeter. This study, using a Perkin-Elmer differential scanning calorimeter Model DSC-2, more precisely defines the heat capacities and entropies of the acids over a somewhat broader concentration range (61.8-83.0% P205)and temperature range (25-370 "C). Materlals and Procedure The most concentrated superphosphoric acid (83.0% P205) was prepared by dissolving reagent P2O5 in reagent H3PO4at This article not subject to
U S . Copyright.
145 'C and fittering the hot solution through a coarse glass frit. Portions of this acid were diluted with reagent H3P04to form acids of the desired concentrations. All the solutions were held overnight at 100 O C to ensure equilibrium distribution of the phosphate species. Final concentrations of the acids were determined by chemical analyses. The acid samples (17.56-29.87 mg) and a synthetic sapphire reference standard (40.09 mg) were hermetically sealed in weighed gold pans. The sample enclosure of the scanning calorimeter was cooled by an aluminum cold finger partially immersed in ice water and was purged continuously with dry nitrogen. The scanning rate for all measurements was 10 deglmin, and the sensitivity of the recorder was 2 mcal s-'. A weiahed emcttv Dan was Dlaced in the sample holder and scannedover the desired temperature range. The empty pan was replaced with the pan containing the sapphire, and it was scanned over the same temperature range. The pan containing the sapphire was then replaced with the pan containing the acid
Published 1981 by the American Chemical Society
Journal of Chemical and Engineering Data, Vol. 26, No. 1, 198 1 71
Table I. Observed Heat Capacities of Phosphoric Acids
61.8% P,O,
cs, C a l
T , K K'' g-'
300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 a
0.4507 0.4584 0.4617 0.4668 0.4710 0.4751 0.4799 0.4844 0.4892 0.4950 0.4990 0.5027 0.5068
SDa
67.0% P,O,
cs, C a l K-lg-'
0.0006 0.0004 0.0004 0.0010 0.0005 0.0008 0.0011 0.0016 0.0017 0.0017 0.0014 0.0015 0.0018
0.4218 0.4276 0.4308 0.4352 0.4394 0.4434 0.4485 0.4532 0.4586 0.4645 0.4694 0.4728 0.4769 0.4808 0.4850 0.4890
SJY'
0.0006 0.0003 0.0004 0.0002 0.0003 0.0004 0.0008 0.001 2 0.0013 0.0011 0.0008 0.0005 0.0006 0.0003 0.0002 0.0006
70.6% P,O,
72.6% P,O,
cs, Cal K-' g-'
SJY'
K-' g-l
SLY
0.3883 0.3916 0.3948 0.3980 0.4018 0.4074 0.41 16 0.4178 0.4252 0.4363 0.4444 0.4448 0.4432 0.4442 0.4470 0.4501 0.4538 0.4573 0.4608
0.0003 0.0006 0.0002 0.0004 0.0007 0.0012 0.0014 0.0022 0.0028 0.0033 0.0033 0.0024 0.001 6 0.0008 0.0008 0.0008 0.0009 0.0005 0.0003
0.3783 0.381 1 0.3855 0.3890 0.3933 0.3976 0.4050 0.4124 0.4233 0.4388 0.4520 0.4540 0.4485 0.4480 0.4509 0.4535 0.4561 0.4599 0.4634 0.4657 0.4681 0.4703 0.4735 0.4754
0.0007 0.0008 0.0005 0.0007 0.0007 0.0009 0.0012 0.0013 0.0020 0.0029 0.0036 0.0014 0.0027 0.0014 0.0017 0.0018 0.0018 0.0019 0.0017 0.0017 0.0014 0.0013 0.0012 0.0014
cs, cal
74.1%P20,
cs,
cs, cal K-l
g-l
0.3675 0.3740 0.3791 0.3831 0.3889 0.3954 0.4014 0.4102 0.4192 0.4290 0.4331 0.4326 0.4350 0.4386 0.4419 0.4454 0.4484 0.4511 0.4536 0.4552 0.4571 0.4586 0.4603 0.4610 0.4628
78.0% P,O,
SI)"
0.0004 0.0004 0.0004 0.0003 0.0005 0.0002 0.0003 0.0002 0.0004 0.0002 0.0001 0.0005 0.0005 0.0007 0.0008 0.0010 0.0010 0.0012 0.0010 0.0011 0.0011 0.0010 0.0008 0.0005 0.0005
g-'
0.3607 0.3642 0.3694 0.3746 0.3783 0.3828 0.3867 0.3906 0.3943 0.3973 0.4005 0.4036 0.4068 0.4093 0.4117 0.4141 0.4172 0.4195 0.4212 0.4226 0.4245 0.4260 0.4274 0.4286 0.4296 0.4305 0.4315 0.4332 0.4338 0.4356 0.4376 0.4396 0.4415 0.4436 0.4468
SDa
0.0004 0.0007 0.0012 0.0014 0.0013 0.0014 0.0016 0.0014 0.001 8 0.0019 0.0022 0.0021 0.0025 0.0028 0.0030 0.0032 0.0033 0.0033 0.0033 0.0033 0.0034 0.0033 0.0033 0.0033 0.0033 0.0034 0.0035 0.0030 0.0033 0.0029 0.0026 0.0025 0.0024 0.0020 0.0021
83.0% P,O,
cs, C a l
K-' g-'
0.3250 0.3286 0.3324 0.3354 0.3382 0.3417 0.3446 0.3476 0.3506 0.3534 0.3559 0.3588 0.361 1 0.3637 0.3660 0.3681 0.3709 0.3727 0.3750 0.3766 0.3786 0.3803 0.3823 0.3838 0.3850 0.3866 0.3882 0.3903 0.3919 0.3936 0.3956 0.3980 0.4004 0.4025 0.4056
SDa
0.0005 0.0003 0.0003 0.0004 0.0006 0.0010 0.001 1 0.0013 0.0015 0.0018 0.0021 0.0023 0.0025 0.0027 0.0029 0.0029 0.0032 0.0034 0.0034 0.0033 0.0033 0.0033 0.0031 0.0031 0.0029 0.0028 0.0027 0.0024 0.0021 0.0018 0.0015 0.0012 0.0008 0.0004 0.0005
SD = standard deviation.
and the scan repeated. The acid sample then was cooled as quickly as possible to the starting temperature and rescanned. The entire procedure was repeated several times for each acid sample, allowing at least 24 h between replicates. The pans containing the acid samples were weighed periodically to ascertain that no weight loss occurred during the measurements. The heat capacities of the acids were determined at even temperature intervals by comparison of the ordinate dlsplacement of the recording of the sample with that of the sapphire, the heat capacity of which is well-known ( Z ) ,according to eq 1, where C,(S) = observed heat capacity of acid (cal deg-' g-'), C,(S) = (WR/WS)[(DS
- DE)/(DR
- DE)]C,(R)
(1)
CJR) = heat capacity of sapphire (cal deg-' g-'), WS = weight of acid sample (mg), WR = weight of sapphire (mg), DS = ordinate displacement of pan plus acid (% of full scale), DR = ordinate displacement of pan plus sapphire (% of full scale), and DE = ordinate displacement of empty pan (% of full scale). Corrections based on the differences in weight between the empty pan and the sample pans and the heat capacity of gold were applied. Heat CapacHy and Enthalpy The average observed heat capacities under the equilibrium vapor pressures, C, at even increments of absolute temperature along with their standard deviations are listed in Table I. An anomaly in the heat-capacity curves, possibly indicating a pronounced redistribution of phosphate species, was observed in the acids of lower concentration (61.8-74.1 % P205) starting at -350 K. The anomaly was rather small with the two acids
Table 11. Enthalpies of Transition of Phosphoric Acids at 350 K concn, %
p20, 61.8 67.0 70.6 72.6 74.1
UTR; cal g-
0.004 0.111 0.974 1.740 0.692
of lowest concentration (61.8-67.0% P205),and no significant differences could be detected between the first scan and the scan immediately after cooling, indicating that equilibrium at the starting temperature was attained quickly upon cooling. The average observed heat capacities for these acids were obtained from all of the scans. The anomaly was more pronounced with three of the acids (70.6, 72.6, and 74.1 % P205),and signifiint differences could be detected in the anomaly between the first scan and the scan immediately after cooling, indicating that, atthough the acids were converting back to the low-temperature form, equilibrium had not been attained. The heat capacitles for these acids at temperatures below and above the anomaly showed no significant differences between the first and second scan: so for these acids, all of the observed heat capacitles at temperatures below and above the anomaly were used to determine the average values. Only those from the first scans were used for the average values in the anomaly. The anomaly was not observed in the heat-capacity curves of the two acids of highest concentration (78.0 and 83.0% P2O5),and no significant differences could be detected between the first and second scans; so for these acids, ail of the observed heat capacities were used to determine the average values. Poly-
72 Joumal of Chemical and Engineerhg Data, Vol. 26, No. 1, 1981
r; 0"
s?" 'Di 34333
n 0 D
5
, */e
P205
Figwe 1. Enthalpy of transition of phosphoric acids. I
0000
I
I
I
I
0000000000
200 o c
'
A
-
0
T= 50
"
A Wok@fl@ldat o 0 Thls Rport
I 65
NP-ww otgwp' ?B.g?
P - W b "
p'mmo
3 0 0 0 ;
B t P Y
0 0 0 0
I 70
m
OC
A
I
I
I
75 PeO, 8 %
80
85
I
-
Figure 2. Enthalpy change above 25
O C
for phosphoric acids.
M
nomial equations of the heat capacity as a functlon of temperature were fitted to the observed values below and above the anomaly. The enthalpies of iransltion, AH,, in cal g-' were determined from eq 2. The first term on the right side of eq
A h=
J,',(CSh dT- f
r
350
(Csh dT
(2)
Jocmei of chemical and Engimsdng Data, voi. 26, No. 1, 1981 73
Table IV. Heat Capacity of Phosphoric Acid, cal g-' "C-' P20,t
T , "C
wt%
62 0.450 0.457 0.462 0.467 0.471 0.478 0.482 0.486 0.491 0.495 0.499 0.504 0.508
25 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 3LO 320 330 340 350 360 370
64 0.441 0.448 0.452 0.457 0.461 0.469 0.473 0.477 0.481 0.486 0.490 0.494 0.498 0.503
66
68
70
72
74
76
78
80
82
0.429 0.436 0.440 0.444 0.448 0.458 0.462 0.466 0.470 0.474 0.478 0.482 0.486 0.490 0.494
0.414 0.420 0.424 0.428 0.432
0.395 0.400 0.403 0.407 0.410 0.426 0.429 0.432 0.436 0.439 0.442 0.446 0.449 0.452 0.456 0.459 0.462 0.465 0.469
0.380 0.386 0.390 0.393 0.397 0.424 0.427 0.430 0.433 0.436 0.439 0.442 0.445 0.448 0.451 0.454 0.457 0.460 0.463 0.466 0.469
0.368 0.376 0.381 0.386 0.391 0.407 0.41 2 0.416 0.421 0.425 0.429 0.433 0.437 0.441 0.444 0.447 0.450 0.453 0.456 0.459 0.461 0.464 0.466 0.468
0.365 0.372 0.376 0.381 0.386 0.392 0.397 0.402 0.406 0.411 0.415 0.419 0.422 0.426 0.429 0.432 0.434 0.437 0.439 0.441 0.442 0.443 0.445 0.445 0.446 0.446 0.446 0.446 0.446
0.360 0.366 0.371 0.375 0.379 0.384 0.388 0.391 0.395 0.399 0.402 0.405 0.408 0.411 0.413 0.416 0.418 0.420 0.421 0.423 0.425 0.426 0.427 0.429 0.430 0.431 0.432 0.434 0.435 0.436 0.438 0.440 0.442 0.445 0.448
0.351 0.358 0.362 0.366 0.369 0.373 0.376 0.379 0.382 0.385 0.381 0.390 0.392 0.394 0.396 0.398 0.400 0.401 0.403 0.405 0.406 0.408 0.409 0.411 0.412 0.414 0.415 0.417 0.419 0.420 0.422 0.4 24 0.426 0.428 0.430
0.337 0.343 0.346 0.350 0.353 0.356 0.359 0.361 0.364 0.366 0.369 0.371 0.373 0.375 0.377 0.379 0.381 0.383 0.384 0.386 0.388 0.390 0.391 0.393 0.395 0.396 0.398 0.40 0 0.40 1 0.403 0.405 0.407 0.409 0.411 0.413
0.444 0.448 0.451 0.455 0.459 0.462 0.466 0.469 0.473 0.477 0.480 0.484
Table V. Enthalpy of Phosphoric Acid, HT - H,5, cal g-'
T,"C 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370
p205,
wt%
62
64
66
68
70
72
74
76
78
80
82
6.8 11.4 16.1 20.7 25.5 30.3 35.1 40.0 44.9 49.9 54.9 60.0
6.7 11.2 15.7 20.3 25.0 29.7 34.4 39.2 44.1 48.9 53.9 58.8 63.8
65 10.9 15.3 19.7 24.3 28.9 33.6 38.3 43.0 47.7 525 57.4 62.2 67.2
6.3 10.5 14.7 19.0 23.6 28.1 32.6 37.1 41.7 46.3 50.9 55.6 60.3 65.1 69.9 74.7
6.0 10.0 14.0 18.1 23.0 27.2 315 35.9 40.3 44.7 49.1 53.6 58.1 62.6 67.2 71.8 76.4 81.1
5.7 9.6 13.5 17.5 23.2 27.5 31.8 36.1 40.4 44.8 49.2 53.6 58.1 62.6 67.1 71.7 76.3 80.9 85.5 90.2
5.6 9.4 13.2 17.1 21.8 25.9 30.1 34.2 38.5 42.7 47.0 51.4 55.8 60.2 64.7 69.2 73.7 78.2 82.8 87.4 92.0 96.7 101.3
55 9.3 13.1 16.9 20.9 24.9 28.9 32.9 37.0 41.1 45.3 49.5 53.7 58.0 62.3 66.6 71.0 75.4 79.8 84.2 88.6 93.0 97.5 101.9 106.4 110.9 115.3 119.8
5.4 9.1 12.9 16.6 20.5 24.3 28.2 32.1 36.1 40.1 44.1 48.2 52.3 56.4 60.6 64.7 68.9 73.1 77.3 81.6 85.8 90.1 94.4 98.7 103.0 107.3 111.6 116.0 120.3 124.7 129.1 133.5 137.9 142.4
5.3 8.9 12.6 16.2 19.9 23.7 27.5 31.3 35.1 39.0 42.8 46.8 50.7 54.6 58.6 62.6 66.6 70.6 74.7 78.7 82.8 86.9 91.0 95.1 99.2 103.4 1075 111.7 115.9 120.1 124.3 128.6 132.9 137.1
5.1 85 12.0 15.5 19.1 22.6 26.2 29.9 335 37.2 40.9 44.6 48.4 52.1 55.9 59.7 63.5 67.4 71.2 75.1 79.0 82.9 86.8 90.7 94.7 98.6 102.6 106.6 110.7 114.7 118.8 122.9 127.0 131.1
J. Chem. EW. Data 1901, 26, 74-80
74
2 was determined by tabular integration of the average observed heat capacities as a function of temperature in the anomaly, and the last term was determined by integratingthe heat capacity equation above the anomaly over the temperature range of the tabular integration. The values for the enthalpy of transition calculated in this manner are listed in Table I1 and shown in Figure 1. Values for heat capacity and enthalpy change above 298.15 K at even intervals of temperature for the phosphoric acMs were calculated from the heatcapacity equations, their integrals with the proper Integration constants, and the heats of transltkn listed in Table 11. These values are listed in Table 111. Enthalpy changes above 298.15 K also were calculated at the same temperatures as those reported by Wakefleld et el. ( 7), and the values compared in Figure 2. The results are in good agreement except at 72.6% P20J,a concentration in which the enthalpy of transition is quite pronounced, and above 350 K (77 "C), the temperature of the transition. This discrepancy probably can be explained by the fact that only the energy released as the acid cools from the higher temperature to 298.15 K in a short period of time would be measured by the drop calorimeter. The slow release of energy as the acid converts from the high-temperature form to the low-temperature form, which takes several hours, would not be detected. Values of heat capacity of the phosphoric acid calculated from the heat-capacity equations were plotted against concentration at each 10degree interval of temperature, and smooth curves were drawn through the points. Values of heat
capacity at each l0-degree interval of temperature for phosphoric acids at even intervals of concentration then were read from the curves. Values of the enthalpy of transition at even intervals of concentration were read from Figure 1. Equations were f i e d to these values, and the heat capacities and enthalpy changes above 298.15 K were determined as described above and are listed in Tables I V and V, respectively. The temperatures were converted to Celsius to make the report compatible with the previous one ( 7). Corrections for converting C, to C,, the heat capacity at constant pressure, based on vapor pressures and enthalpies of vaporization taken from the literature (3)and the assumption that the liquids occupied 75% of the encapsulated volumes were less than 0.001 cal deg-' 9-l over most of the temperature ranges but did increase to 0.002 cal deg-' g-l when the liquids were near their boiling points. These corrections, approximately the same magnitude as the differences between the observed and calculated heat capacitles, were considered to be within the precision of the measurements. Literature Cited (1) Wakefield, Z. T.; Luff, B. B.; Reed, R. 6. J . Chem. €ng, Data 1972, 17, 420-3. (2) (Ynnings, D. C.; Fwukawa, G. T. J. Am. Chem. Soc. 1959, 75, 522-7. (3) Brown, E. H.; WMtl, C. D. Ind. Eng. Chem. 1952, 44. 615-8.
Recelved for review June 2, 1980. Accepted October 27, 1980.
Solubitity of Acetone and Isopropyl Ether in Compressed Nitrogen, Methane, and Carbon Dioxide Paul J. Hicks, Jr., and John M. PrausnRz" Chemical Engineering Department, Universw of Californie, Berkeky, Californie 94 720 Vapor-phase eolubllitles are reported for acetone and Isopropyl ether In compressed nitrogen, methane, and carbon dioxlde, In the range -50 to 50 O C and 17-63 bar. The experimental sduMlitks are reduced to obtain second vlrlal cross-coeffidents. Experimental crosrccoeftlclents are compared to those calculated by wlng the square-well potentla1 or the Hayden-O'Cormdl corrdatbn. There is lile fundamental information concerning the interaction between a smaH nonpolar molecule (2)and a large polar molecule ( 7). To obtain such information, it is useful to measure the second virial cross-coefficient BI2 which is directly This work reports related to the intermolecular potential r12. experimental measurements which yield B12for a number of binary polar-nonpolar mixtures. The experimental data obtained are the solubilities of acetone and isopropyl ether in compressed nitrogen, methane, and carbon dioxide. These measurements are also of interest in chemical engineering because they provide the fundamental information needed to calculate solvent losses in an absorption process operating at advanced pressure. This work is similar to that of Lazalde et el. ( 7), who studied the solubility of methanol in compressed gases. Experimental Sectlon The experimental apparatus is similar to that used by Larelde There are some minor modifications made primarily to
( 7).
0021-9568/81/ 1726-0074$01.00/0
facilitate changing pressures In the apparatus. A schematic of the flow apparatus is shown in Figure 1. A light (gaseous) component is equilibrated with a heavy (liquld) component at a given temperature and pressure. The gas phase is sampled and analyzed. The llght component is fed from a gas cylinder through a pressure regulator and a precooling/preheatlng coil to the two equilibrium cells arranged in series. The gas enters the bottom of each equillbrlum cell, containing the liquid being studied, through a stainless-steel sparger whose average pore size is 5 pm. The slowly flowing gas is saturated with the liquid as it bubbles through the liquid. Two cells in series are used to ensure that the exiting gas is in equilibrium with the liquid. The top of each cell Is packed with glass wool to remove any possible entrainment of the llquid in the gas. The gas exits the second cell through a section of tubing heated to prevent condensation of the heavy component. In this section the gas is expanded to atmospheric pressure. The volumetrlc flow rate is always less than 0.3 cm3/swhere the measured solubility is independent of the flow rate. The constant-temperature bath containing the equilibrlum cells is controlled by a HalHkainen (Shell Development) thermotrol to 10.05 OC or better except at -50 OC where it is controlled to 10.15 O C or better. At low temperatures, the bath fluid is 95% ethanol; at high temperatures, it is water. Temperatures above -10 O C are measured with a set of Ilquid-inglass calorimetric thermometers with an accuracy of io.1 OC. Temperatures between -10 and -25 OC are measured with a
@ 1981 Amerlcan Chemical Society
